Strange diagnostic pictures on boot

Mac Mini 2010 version running Mavericks

Have just replaced the PRAM battery. Two mistakes during the job. First the optical drive thermal sensor socket came loose in stage 15 of the iFixit instructions. Second, I discovered I had a non-rechargeable battery but changed the battery anyway.

Tried gluing the socket back to the logic board, which looked as though it was successful.

However, when restarting the machine, the fan started hissing and there was a noticeable draught from the opening. The machine appears to start to the rotating lines, but instead of booting two pictures start to oscillate. One shows an oval shape with a rectangle inside. At the top right is another small oval which is the focus of an enlargement and appears to indicate that a switch should be moved up. The other shows an inclined plane (could be a computer keyboard) with a cylinder at the right, and on the cylinder end is an on-off switch which is indicated by an arrow.

Any ideas welcome.

Later note: I went back in and nudged the optical drive sensor, and the fan activity stopped. Unfortunately the computer will still not boot normally but goes to showing the above two pictures alternately. Still looking for suggestions. Have not had any from the iFixit forum. Anybody know what these two pictures mean?